1. Field of the Invention
The present invention provides a method of olefin polymerization that allows for production of monomodal polyolefins of very narrow molecular weight polydispersity and of tunable composition and molecular weight. The olefin polymerization process is further defined as a ‘living’ polymerization that is mediated by an ‘active’ transition metal catalyst that serves as the propagating center for chain growth through monomer enchainment. According to prior art, a living polymerization is further defined as one in which there is a requisite limitation of one polymer chain per active propagation. The present invention however removes this limitation by including additional equivalents of a main group metal alkyl that serve as additional ‘surrogate’ chain growth sites through highly efficient and reversible polymer chain-transfer between the active propagating transition metal center and the surrogate main group metal sites. This new polymerization process is uniquely defined as ‘living coordinative chain-transfer polymerization’ of olefins and it additionally allows for the first time, scalability of the volume of polyolefins that can be prepared through living polymerization with a dramatic reduction in the amount of transition metal catalyst that is required while not sacrificing all the desired beneficial features of the polymer that can be obtained through a living process, including tunable molecular weights, narrow polydispersities, ability to prepare block copolymers with discrete block junctions, random copolymers, and polyolefins with well-defined and discrete end-group functionalizations.
2. Related Art
Several transition-metal-based catalysts have been reported that can mediate the living metal-mediated coordination polymerization (also known as homogeneous, single-site Ziegler-Natta polymerization) of ethene, propene, higher α-olefins, and α,ω-nonconjugated dienes, and, in some cases, these proceed with a high degree of stereocontrol (tacticity) ((for a review of catalysts for living coordination polymerization of ethene and α-olefins, see: Coates, G. W., et al., Angew. Chem. Int. Ed. 41:2236-2257 (2002)); (for the living and stereoselective coordination polymerization of α-olefins and α,ω-non-conjugated dienes, see: Jayaratne, K. C., et al., J. Am. Chem. Soc. 122:958-959 (2000)); Jayaratne, K. C., et al., J. Am. Chem. Soc. 122:10490-10491 (2000); Keaton, R. J., et al., J. Am. Chem. Soc. 123:6197-6198 (2001); Zhang, Y., et al., Chem. Commun. 2358-2359 (2003); Zhang, Y., et al., Organometallics 23:3512-3520 (2004); Harney, M. B., et al., Angew. Chem. Int. Ed. 45:2400-2404 (2006); Harney, M. B., et al., Angew. Chem. Int. Ed. 45:6140-6144 (2006); Zhang, W., et al., Adv. Synth. Catal. 350:439-447 (2008)). However, the commercialization of new polyolefin materials and products that take advantage of the unique capabilities of living coordination polymerizations appears unlikely ((for reviews of polyolefin materials prepared through living coordination polymerization, see: Domski, G. J., et al., Prog. Polym. Sci. 32:30-92 (2007); Sakuma, A., et al., Polym. J. 39:193-207 (2007)); Szwarc, M., et al., Ionic Polymerization and Living Polymers; Chapman & Hall: New York (1993); Quirk, R. P., et al., Polym. Int. 27:359-367 (1992); Matyjaszewski, K., J. Phys. Org. Chem. 8:197-207 (1995)).
The same fundamental criterion of a living polymerization, namely, chain-growth propagation in the absence of irreversible chain termination, serves to establish a ‘one polymer chain per active metal center’ cap on product yield as a critical liability. The severity of this liability sharply increases as the targeted number-average degree of polymerization, Xn, of the desired polyolefin product decreases. While living coordination polymerization is ideally suited for accessing the largely unexplored material science and technology associated with architecturally well-structured ‘precision polyolefins’ of very low to moderate molecular weights (ca 500-10,000 Da), the practical availability of significant quantities of these materials presently remains out of reach due to unfavorable weight (polymer) to weight (catalyst) ratios ((for a review of catalysts for living coordination polymerization of ethene and α-olefins, see Coates, G. W., et al., Angew. Chem. Int. Ed. 41:2236-2257 (2002)); (for reviews of polyolefin materials prepared through living coordination polymerization, see Domski, G. J., et al., Prog. Polym. Sci. 32:30-92 (2007); Sakuma, A., et al., Polym. J. 39:193-207 (2007)); Szwarc, M., et al., Ionic Polymerization and Living Polymers; Chapman & Hall: New York (1993); Quirk, R. P., et al., Polym. Int. 27:359-367 (1992); Matyjaszewski, K., J. Phys. Org. Chem. 8:197-207 (1995); Kaneyoshi, H., et al., Macromolecules 38:5425-5435 (2005); Ring, J. O., et al., Macromol. Chem. Phys. 208:896-902 (2007); Ventola, L., et al., J. Phys. Chem. Solids 66:1668-1674 (2005)).
There is a need, therefore, for new methods of coordination polymerization of olefins that allows for scalability of the volume of polyolefins that can be prepared through living polymerization with a dramatic reduction in the amount of transition metal catalyst that is required while not sacrificing all the desired beneficial features of the polymer that can be obtained through a living process, including tunable molecular weights, narrow polydispersities, ability to prepare block copolymers with discrete block junctions, random copolymers, and polyolefins with well-defined and discrete end-group functionalizations.